1) Field of the Invention
The field of the invention pertains to methods and apparatus for implementing a control network and, more particularly, to a network node for use in a control network.
2) Background
Automated control systems are commonly used in a number of manufacturing, transportation, and other applications, and are particularly useful to control machinery, sensors, electronics, and other system components. For example, manufacturing or vehicular systems may be outfitted with a variety of sensors and automated electrical and/or mechanical parts that require enablement or activation when needed to perform their predefined functions. Such systems commonly require that functions or procedures be carried out in a prescribed order or with a level of responsiveness that precludes sole reliance on manual control. Also, such systems may employ sensors or other components that require continuous or periodic monitoring and therefore lend themselves to automated control.
As the tasks performed by machinery have grown in number and complexity, a need has arisen for ways to exercise control over the various components of a system rapidly, efficiently and reliably. The sheer number of system components to be monitored, enabled, disabled, activated, deactivated, adjusted or otherwise controlled can lead to difficulties in designing and implementing a suitable control system. As the number of system components to be controlled is increased, not only is the operation of the control system made more complicated, but also the wiring and inter-connections of the control system are likewise more elaborate. In addition, greater reliance on automated control has resulted in larger potential consequences if the automated control system fails.
Certain conventional types of distributed control network use a hierarchical control structure with nodes to handle local tasks. For example, one type of control network uses a dual-bus architecture including a primary bus for a high-speed, bi-directional communication link interconnecting a main (or first-tier) data bus controller with distributed slave nodes. One of the slave nodes acts as a second-tier data bus controller connected to a secondary, low-speed data bus. A number of second-tier slave nodes may be connected to the secondary data bus. The first-tier and second-tier slave nodes may be connected to various input/output ports for performing various local functions. The main data bus controller, secondary data bus controller, first-tier slave nodes, second-tier slave nodes, input/output ports and other system components collectively form a hierarchical system wherein the main data bus controller supervises the first-tier slave nodes, including the second data bus controller, the second data bus controller supervises the second-tier slave nodes, and the first-tier slave nodes and second-tier slave nodes supervise their assigned input/output functions.
A more elaborate control network system as conventionally known is described, for example, in U.S. Pat. No. 5,907,486, assigned to the assignee of the present invention. In the system described therein, additional data buses may be added to the hierarchical control network, so as to form additional second-tier control loops each having a secondary data bus controller (master node) and a set of second-tier slave nodes, and/or additional lower-tier control loops, each having an Nth-tier data bus controller (master node) and a set of Nth-tier slave nodes.
A problem that particularly affects large, distributed control networks is re-configuring the system when network nodes are replaced or added. A network node may be replaced because it has failed electrically, or because additional functionality is needed, or may be added to increase the capability or size of the control network. Each network node requires a unique identifier, so it can be referenced by the other nodes. Each network node is also required to be programmed with its specific functionality. As currently practiced, when network nodes are replaced, a computer or special tool is needed to download the node identifier and/or functional program code to the node. This task requires specialized equipment, and is time-consuming and inconvenient. Moreover, a mistake can be made in entering the node identifier manually, which will cause the system to function improperly thereafter.
Likewise, when an existing network node needs to be reprogrammed to change its functionality, the same sort of specialized equipment is needed to download the new program or change the program parameters. Again, this task is time-consuming and inconvenient.
Accordingly, it would be advantageous to provide a mechanism for allowing rapid and convenient association of a network node with a node identifier, and rapid and convenient programming of a newly added or existing network node.